Typically, a solid oxide fuel cell (SOFC) employs a solid electrolyte of ion-conductive oxide such as stabilized zirconia. The solid electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly. The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, normally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
As the fuel gas supplied to the fuel cell, normally, a hydrogen gas produced from hydrocarbon raw material by a reformer is used. In general, in the reformer, a reformed raw material gas is obtained from hydrocarbon raw material of a fossil fuel or the like, such as methane or LNG, and the reformed raw material gas undergoes steam reforming, partial oxidation reforming, or autothermal reforming to produce a reformed gas (fuel gas).
In this regard, a fuel cell system (fuel cell apparatus) having a single unit case containing a fuel cell, a reformer, a power converter for converting direct power electrical energy generated in the fuel cell according to a power supply output specification, a control device, and auxiliary devices is known.
In particular, in the case where a high temperature fuel cell (such as a solid oxide fuel cell or a molten carbonate fuel cell) or a medium temperature fuel cell (such as a phosphoric acid fuel cell and a hydrogen membrane fuel cell) is used, the temperature in the unit case tends to be considerably high. However, the temperature of the atmosphere around the power converter, the control device, and the auxiliary devices needs to be maintained at relatively low temperature for preventing degradation in the performance and reduction in the product life.
For example, in a packaged fuel cell power generator apparatus disclosed in Japanese Laid-Open Patent Publication No. 04-075263, as shown in FIG. 20, a package 1 is provided. The package 1 includes an upstream side package chamber 1A and a downstream side package chamber 1B. The upstream side package chamber 1A has a ventilation fan 3 at an intake port for intake of the external air. The downstream side package chamber 1B is connected to a ventilation discharge port of the upstream side package chamber 1A through a coupling duct 1C.
The upstream side package chamber 1A contains therein a power converter unit 4 including a chopper 4A, an inverter 4B and a controller 4C. The downstream side package chamber 1B contains therein a fuel cell unit 8 including a fuel cell 5, a reactant air blower 6A, a combustion air blower 6B, and a fuel reformer 7.
The air at normal temperature supplied into the upstream side package chamber 1A by the ventilation fan 3 cools the power converter unit 4 by ventilation, and then, the air is supplied to the downstream side package chamber 1B through the coupling duct 1C. After the air is used for cooling and ventilation of the fuel cell unit 8, the air is discharged to the outside through an exhaust port 9.
Further, in a ventilating structure of a packaged fuel cell power generator apparatus disclosed in Japanese Laid-Open Patent Publication No. 05-290868, as shown in FIG. 21, a package 1a is provided. The space in the package 1a is divided by a heat insulating partition 3a having a ventilation hole 2a into a high temperature device chamber 4a and an electrical device chamber 4b. There is formed a ventilation port 5a for intake of the external air, on the outer wall of the electrical device chamber 4b. The high temperature device chamber 4a contains therein a fuel cell 6a and a fuel cell reformer 7a. 
The high temperature device chamber 4a contains therein a reactant air blower 6b connected to the fuel cell 6a, and the electrical device chamber 4b contains therein a fuel air blower 7b connected to the fuel cell reformer 7a. The electrical device chamber 4b contains therein a power converter 8a, a measurement controller 8b, auxiliary devices 8c, and a raw fuel tank 8d. It is required to control the temperature of the atmosphere around these devices in the electrical device chamber 4b. 
In this package 1a, in the presence of the heat insulating partition 3a, the electrical device chamber 4b is not influenced by the heat from the high temperature device chamber 4a. Further, according to the disclosure, the external air at normal temperature is sucked through the ventilation port 5a into the electrical device chamber 4b for forced ventilation in the electrical device chamber 4b to lower the temperature of the atmosphere around the power converter 8a, the measurement controller 8b, the auxiliary devices 8c, the raw fuel tank 8d or the like.